Sumerian, Language Families
Standing
Concerns Homeland Hypothesis
Currently States Southern Mesopotamia itself, on the reading that Sumerian speakers were there from the settlement of the marsh country, against the older proposal that they arrived from elsewhere and absorbed an earlier population. Neither can be shown from the language, because it has no demonstrated relative to place it beside.
Marie-Louise Thomsen's scholarly grammar records two competing accounts of where Sumerian speakers originated: that they were already present in southern Mesopotamia from the earliest settlement of the marsh country, and an older proposal, associated with early twentieth-century Assyriology, that they migrated into the region from elsewhere and absorbed an earlier, non-Sumerian-speaking population already living there. Both readings point to features of the language itself, including a substantial layer of vocabulary for cities, rivers, crafts and occupations that resists explanation from within Sumerian, as evidence, the indigenous reading treating it as simply old inherited vocabulary and the migration reading treating it as borrowed from the absorbed population. Neither can be demonstrated, because Sumerian is a language isolate with no demonstrated living or ancient relative against which to compare its vocabulary and test either story; the same unexplained vocabulary is compatible with both accounts and there is no external control to choose between them. The question is treated as open rather than as leaning toward either side because it depends entirely on evidence internal to a single, unrelated language.
Source The Sumerian Language: An Introduction to Its History and Grammatical Structure, Marie-Louise Thomsen